This invention relates to an intake gas resonance system for improving the intake gas supply of reciprocating piston-type internal combustion engines. In the system, for the purpose of increasing the charging of the cylinders with intake gas, a determined group of cylinders is coupled, as a unit, by means of a short suction pipe, to a resonator vessel and further, a resonance tube communicates with the resonator vessel.
Internal combustion engines of the reciprocating piston type are known wherein the intake gas supplying system, in order to increase the charging of the cylinders, utilizes the energy of the gas oscillations generated by the periodic suction effect of the engine cylinders. A conventional solution resides in the so-called suction pipe charging wherein the intake opening of each engine cylinder is coupled with a suction pipe/resonance tube or predetermined cross section and length. Such a system is discussed in an article by D. Broome, entitled "Induction Ram", in The Automobile Engineer/London GB/, 1969, issue 4-6. In such intake gas supplying systems the depression wave generated by the suction effect of the engine cylinder propagates--as known--close to the speed of sound along the length of the suction pipe and, at the open end thereof, it is reflected as a compression wave. As known, reflection is effected also at that pipe end which adjoins the intake opening of the cylinder; the amplitude of the wave reflected there, however, depends from the momentary flow passage cross section of the intake opening. If the back-and-forth travelling time of the wave, that is, the natural frequency of the gas column is appropriately tuned with the displacement of the respective engine piston, at the end of the intake cycle a compression wave reaches the cylinder and in this manner more intake air is driven at a higher pressure into the cylinder. The propagation time of the wave natural frequency is determined, in addition to the speed of propagation, which is close to the speed of sound, by the distance for a back-and-forth travel of the wave. Stated differently, the time of propagation is determined by the length of the suction pipe. Consequently, in an intake gas resonance system, the length of the suction pipe is one of the most important factors for improving the intake gas supply. The cross section of the suction pipe affects particularly the developing speed and thus the level of the kinetic energy present in the pipe due to the non-stationary oscillating process. The pipe cross section, dependent upon the given requirements, has a determinable optimum value.
For a favorable course of the oscillation phenomena a substantially uniform pipe cross section is needed because the compression waves are reflected not only from the open end of the pipe or from the so-called closed end which is adjoining the intake opening of the cylinder or from a partially closed pipe end, but reflection also takes place at all locations where the cross section of the pipe widens or narrows. This phenomenon is described on page 41 of a book authored by H. Seifert and entitled "Instationare Stromungsvorgange in Rohrleitungen an Verbrennungskraftmaschinen" (Non-Stationary Flow Phenomena in Pipe Conduits of Combustion Engines), published by Springer Verlag, 1962. The pipe length determined by the requirements for a favorable operation thus has to be ensured while maintaining the pipe cross section uniform.
In certain states of the oscillating process the velocity of the medium flowing in the suction pipe resonance tube changes direction and the medium flows out at the open end of the pipe. This results in a loss of the kinetic energy of the exiting air jet. Heretofore it was not practically feasible to reduce these losses.
It is, to be sure, thinkable to theoretically couple, to the suction pipe portion of uniform cross section, as a continuation thereof, a pipe portion which widens towards the open pipe end diffuser to make possible the recovery of one part of the lost kinetic energy. Such a diffuser, however, would even further increase the already inconveniently great length of the suction pipe. The length increase caused by the widening pipe portion would make the structural accommodation of the suction pipes and the entire intake gas supply system unfeasible in the space available next to the engine, under the hood of the vehicle. Consequently, such solutions have not been materialized in practice.
There are further known reciprocating piston-type internal combustion engines in which the intake gas system for improving the intake gas supply is so designed that between the intake opening of a determined group of cylinders and the resonance tube a resonator vessel of determined volume is arranged as described, for example, in Hungarian Pat. No. 161,323 and German Pat. No. 1,935,155. Such intake gas system is termed as a resonance system and the charging process itself is termed as resonance charging. The resonance charging may be advantageously used not only in naturally aspirating engines; the resonance intake gas system is also effective if arranged between the engine and a charging device such as a turbo supercharger. This type of arrangement is termed as combined charging.
The medium flowing in the resonance system is excited by the periodic suction effect of the group of those engine cylinders coupled to the resonator vessel, whose suction cycles do not significantly overlap one another. In case the frequency of the excitation equals the natural frequency of the resonance system, a resonance is generated in the intake gas system and the increased oscillations charge the engine cylinders to a significant extent.
At a given dimensional ratio between the individual elements of the resonance system the gas oscillations increase the charging of the cylinders not only for that rpm where resonance appears but also in a wide rpm range as described in Austrian Pat. No. 330,506 and British Pat. No. 1,400,059. It is to be noted that the greatest charging effect, however, appears at the resonance value. It is an advantageous property of the system that the resonance can be set not only for a high engine rpm but, with an appropriate alteration of the natural frequency of the resonance system, even at very low rpm's the intake gas supply may be improved without the system having an adverse effect on the operation of the engine at high rpm's.
The natural frequency of the medium flowing in the resonance system depends--as a departure from the earlier-mentioned suction pipe charging--not only from the length of the resonance tube of uniform cross section but also from its cross section and the dimension of the resonating volume. These relationships are discussed in an article by F. Anisits and F. Spinnler, entitled "Entwicklung der Kombinierten Aufladung am neuen Saurer-Fahrzeugdieselmotor D 4KT" (Developments of the Combined Charging in the New Saurer Vehicle Diesel Engine D 4KT), in Motor-Technische Zeitschrift, Stuttgart, FRG, 1978. issue 10. The dimensions and relationships required for obtaining the desired natural frequency and desired for a favorable operation--as discussed in Austrian Pat. No. 330.506--can be maintained, however, only under limitations which make a structural realization of the resonance system as well as the accommodation of the resonance system in the space available at the engine exceedingly difficult. The structural accommodation of the resonator vessels and particularly of the resonance tubes of predetermined dimensions became prime considerations in the practical application of the resonance system. Useful considerations to resolve various problems involved in this connection are discussed in Hungarian Pat. Nos. 173,034 and 175,875 as well as U.S. Pat. No. 4,064,696 as well as German Offenlegungsschrift No. 2,831,985. While the above-noted arrangements favorably utilize the space available adjacent an in-line six-cylinder engine, none of the solutions was able to address the problem of excessive dimensions required for a favorable operation. This means that the spatial requirement even of advantageously arranged structures is substantial which, in many cases, constitutes an obstacle for their practical application.